The Wall Street Journal spoke with an unnamed Hon Hai executive today about why the iPhone 5 is experiencing supply shortages, and the Taiwanese manufacturer, also known as Foxconn, apparently blamed it on the smartphone’s complicated design and its subsequent assembly process.

“The iPhone 5 is the most difficult device that Foxconn has ever assembled. To make it light and thin, the design is very complicated,” said the executive to the Wall Street Journal. “It takes time to learn how to make this new device. Practice makes perfect. Our productivity has been improving day by day.”

The official did not wish to be named, but he admitted Hon Hai is attempting to better production capacity while apply more procedures to alleviate the reports of damages such as scratches to the iPhone 5’s metal casing.

Apple’s latest smartphone is currently assembled at Hon Hai’s plants in Zhengzhou and Guan Lan, China. The executive further attributed the recent conflict between assembly line workers and quality inspectors in Zhengzhou last month to the metal casing and other quality-check issues:

“The Zhengzhou site, which was set up in 2011, is still pretty new to us. We are still learning how to manage the work force there,” the executive explained, adding Hon Hai has increased hiring at the plant to continue boosting production.